On Wed, 24 Jun 2009, Marcelo Leal wrote:
I think that is the purpose of the current implementation:
http://blogs.sun.com/roch/entry/the_new_zfs_write_throttle But seems
like is not that easy... as i did understand what Roch said, seems
like the cause is not always a "hardy" writer.
I see this:
"The new code keeps track of the amount of data accepted in a TXG and
the time it takes to sync. It dynamically adjusts that amount so that
each TXG sync takes about 5 seconds (txg_time variable). It also
clamps the limit to no more than 1/8th of physical memory."
It is interesting that it was decided that a TXG sync should take 5
seconds by default. That does seem to be about what I am seeing here.
There is no mention of the devastation to the I/O channel which occurs
if the kernel writes 5 seconds worth of data (e.g. 2GB) as fast as
possible on a system using mirroring (2GB becomes 4GB of writes). If
it writes 5 seconds of data as fast as possible, then it seems that
this blocks any opportunity to read more data so that application
processing can continue during the TXG sync.
Bob
--
Bob Friesenhahn
bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
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